This application relates to the preparation of the cyanates of alkali metals and alkaline earth metals. It is well known to prepare alkali metal and alkaline-earth metal cyanates using various methods, however, none of these known methods is satisfactory in every respect as each has its inherent drawbacks.
For instance, it is possible according to British Patent Specification No. 339,220 to prepare salts of cyanic acid by heating urea above its melting point with oxides, hydroxides or carbonates of alkali metals or alkaline-earth metals in the absence of solvents. In this process, however, the yield obtained is low because water is liberated during the reaction, and the thus liberated water, under reaction conditions, partly hydrolyzes the cyanate formed. For instance, when a metal hydroxide is used as the starting material 1 mole of water is liberated for every equivalent of cyanate formed, which, in turn, accounts for the hydrolysis of 0.5 mole equivalent of cyanate, so that, in the net reaction, the overall cyanate yield does not reach much beyond 50 percent. Another disadvantage of this known process is that, in practice, handling the urea melt involves technological difficulties.
According to another process described in British Patent Specification No. 354,604 ammonium cyanate is converted with a metal-oxide or metal-hydroxide in the presence of aliphatic monoalcohols or liquid ammonia. Even at a relatively low temperature this reaction proceeds at a sufficient rate, the hydrolysis rate of the cyanate product formed being minimal at the low temperature. Therefore, the presence of a small amount of water, contrary to the urea process, is not disastrous in that case. However, this process does have the disadvantage in that ammonium cyanate must first be prepared and isolated and this preliminary procedure substantially adds to the cost price of the metal cyanate to be prepared. Moreover, the introduction of a substance which itself is not one of the reactants, like an aliphatic monoalcohol, renders operational control of the reaction more complex.
An object of the present invention is to provide a process for preparing salts of cyanic acid which avoids these drawbacks as well as other disadvantages, and which also offers other specific advantage over prior procedures.